1. Field of the Invention
This invention relates to a switch device, and more particularly to an improved switch device capable of detecting and indicating operational failure or trouble thereof.
2. Description of the Prior Art
Mechanical switches for controlling the operation of electrical circuits are used in a wide variety of applications. Among those applications is a production or assembly line in an unmanned, automated factory where the switch devices are employed to mechanically detect the passage of various products in the making or workpieces through predetermined process locations along the line for controlling related machineries and mechanisms. Conventionally, limit switches are widely used for this purpose. The limit switch for detecting the passage movement of workpieces or other objects typically includes a self-contained spring mechanism and a movable actuator to be brought into contact with the passing objects. As the approaching object comes into contact with the actuator, the actuator is moved or rotated in one direction. As the object moves away, the actuator is rotated back in the opposed direction under the biasing force of the spring mechanism. This back and forth movement of the actuator drives the limited switch into ON and OFF positions or open and closed positions.
The conventional switches for use in the factory production line, however, have some drawbacks. For example, the associated actuator mechanism is sometimes rendered in immobile due to an increased internal friction. A seal failure in the switch casing permits moisture to penetrate, thereby causing electrical shortings within the switch. Switch contacts being melted together and or accumulation of dusty particles on the switch contacts may also result in a faulty ON-OFF operation of the switch. The malfunction or failure of the limit switch, in turn, leads to the disruption in the operation of the entire production line, and, thus, defective products. In order to correct these situations, the malfunctioning limit switch have to be repaired or exchanged with a new one while keeping the production line at a brief standstill. Shut-down of the production line, however brief, will have an immense influence on the entire manufacturing activity and result in a remarkable reduction of production efficiency.
Various attempts have been proposed to overcome the problems inherent in the prior art limit switch. For example, in order to obtain a reliable ON-OFF switching action, it has been taught to incorporate into the limit switch some means for protecting the switch contact against melting together. It has also been proposed to forcefully separate the melted switch contacts apart. However, there have never been effective solutions proposed for the above mentioned problems such as the switch actuator being made immovable by the increased internal friction, and the dusty materials on or between the switch contacts blocking the normal closing of the contact. Accordingly, any trouble or failure in the operation of the limit switch still costs the costly shut-down of the entire production lines.